1. Field of the Invention
The present invention relates to the fields of diagnostic and therapeutic cardiology. More specifically, the present invention relates to, inter alia, methods for diagnosing and managing venous thromboembolism and intracardiac thrombi.
2. Description of the Related Art
Fibrinolysis is the process of degradation of fibrin in the blood. Fibrinolysis is involved in a number of physiopathological processes and is triggered in situations when tissue plasminogen activator (t-PA) and plasminogen bind to fibrin, forming a fibrin-plasminogen complex within which the t-PA has a high affinity for plasminogen, entraining the generation of plasmin, a key enzyme which degrades fibrin into D-dimers.
Degradation of fibrin, or fibrinolysis, leads to the formation of degradation products especially comprising “D-dimer” fragments, the major degradation products of cross-linked fibrin.
The fibrin undergoing the fibrinolysis process is formed by conversion of fibrinogen under the action of the coagulation enzyme thrombin. Upon activation of the coagulation system, thrombin cleaves fibrinogen, opening the polymerizing sites and generating fibrin soluble monomer along with fibrin protofibrils. To accomplish this, thrombin attacks four peptide bonds of the fibrinogen located respectively on the 2 A alpha and the 2 B beta chains, causing the liberation of two A fibrinopeptides from the two A alpha chains and the liberation of two B fibrinopeptides from the B beta chains, resulting in the formation of fibrin monomers which polymerize spontaneously into the form of a polymer by dint of hydrogen bonds established by interaction between A and B polymerization sites unmasked during liberation of the A and B fibrinopeptides and the a and b sites which are available at the ends of the gamma and beta chains respectively. The fibrin polymer is then immediately stabilized by factor XIII(a), forming insoluble cross-linked fibrin, the main component of thrombi. Thrombin generation is much greater during in vitro tests than that which takes place in vivo. For this reason, the generation of fibrin monomers is much slower in the in vivo coagulation activation process than in that generated in vitro.
Determining the concentration of soluble fibrin monomer of fibrinopeptides is important in order to estimate the degree of coagulation up-regulation in a patient. The increased level of soluble fibrin monomer will represent thrombin overactivity and will be associated with a cleavage of fibrinogen. This determination may be carried out using samples of blood or plasma obtained from a blood sample taken from a patient.
Assaying soluble fibrin monomer of fibrinopeptides is a useful complement to plasma fibrinolytic status since soluble fibrin monomer is a marker of thrombotic event and up-regulation of coagulation which is under way while the concentration of fibrin degradation products (particularly D-dimer) indicates degradation of a thrombus, even if the activation of coagulation process is stopped. In summary, the plasma level of fibrin degradation products or D-dimer is increased while the fibrin clot degrades in vivo. Hence, if the thrombus is present and undergoing degradation, the level of D-dimers is high, whether coagulation persists or is stopped. In contrast, the level of soluble fibrin is raised only if coagulation persists.
Commercially available D-dimer assays are limited to detection of only single D-dimer structure. The interference with other fibrin degradation products are mostly excluded as the antibody used is specific only for a neo-antigen on the D-Dimer structure. Thus, determining the level of D-dimers in the sample, termed the base level, is a reflection of the degradation of the thrombus which occurs in vivo, while further cleavage of soluble fibrin degradation products in vitro or in vivo with exogenic addition of a specific fibrin thrombolytic agent results in profound fibrinolysis and completed release of D-dimer from multimeric fibrin degradation products. The final level of D-dimer represents the sum of the base D-dimers and the D-dimers deriving from degradation of fibrin degradation products and soluble complexes of D-Dimer or fibrin degradation products with fibrin monomer, also termed circulating fibrin.
Venous thromboembolism (VTE) is a common but diagnostically challenging illness that can cause significant disability and death if not promptly diagnosed and effectively treated. About 2 to 3 million individuals in the US develop VTE every year and of those, 60,000 die, primarily from pulmonary embolism (PE). Acute PE is a common and often fatal disease with a mortality rate of 30% without treatment. While mortality can be reduced by prompt diagnosis and therapy, it is estimated that more than half of all patients with PE remain undiagnosed. The magnitude of VTE as a clinical problem can be attributed to gaps in the understanding of pathogenic mechanisms, the wide variety in patient presentations, and limited diagnostic and therapeutic options. The D-dimer test is currently used to diagnose VTE in clinical practice, which measures the dimeric forms of the fibrin degradation products using an antigen-antibody reaction.
In 2005, using a swine model, it was shown that mini-dose tPA could lyse in situ thrombus in the femoral vein of swine, allowing increased sensitivity of D-dimer for detecting in situ venous thrombus in swine. This, however, did not address the problem of diagnosing venous thromboembolism in humans. Currently in humans, the problem is poor specificity and poor positive predictive value of a positive current D-dimer test. This pig study was designed to improve sensitivity when D-dimer did not detect clot.
Thromboembolic venous diseases principally comprise venous thromboses of the limbs and pulmonary embolism, the latter resulting from a complication of the first thromboses. Venous thromboses other than those of the limbs are also encountered, since all venous territories can undergo a thrombosis. The renal veins and mesenteric veins can be cited in particular among those which are at the origin of pathologies. Thromboembolic diseases such as deep venous thrombosis (DVT) and/or pulmonary embolism (PE) are life-threatening diseases and represent a large proportion of the disabilities and deaths in industrialized countries, and establishing a diagnosis of these diseases is vital in completing investigations by imaging examinations such as ultrasound imaging for the diagnosis of venous thromboses and scintography or angiography to diagnose pulmonary embolisms. These imaging methods are expensive, carry significant morbidity and hence are deployed late in the diagnostic process. Since the disease process is so variable from asymptomatic to life threatening prompt and accurate diagnosis is vital and can improve mortality significantly.
As a result, there is a continuing need for defining a test allowing rapid diagnosis of thromboembolic disease in a patient, that diagnosis including the possibility of excluding that disease without necessarily having recourse to additional investigations. Thus, there is a continued need in the art for improved methods and therapies to diagnose and treat venous thromboembolism and intracardiac thrombi. The present invention fulfills this long standing need and desire in the art.